1. Field of the Invention
The present invention relates to a method and an apparatus for forming a three-dimensional image of a pattern to be inspected, and more particularly, to a method of forming a three-dimensional image of a pattern using X-rays without fracturing the pattern.
2. Description of the Related Art
As semiconductor devices are becoming highly integrated and are operating at higher speeds, design rule requirements and contact areas of the devices are being continuously reduced. This reduction has lead to requirements to form a finer pattern and a smaller contact hole on the pattern. The fine pattern and smaller contact hole require an improved measuring technology for detecting a critical dimension or a processing defect thereof. Furthermore, the fine pattern and smaller contact hole require a novel measuring technology fundamentally different from a conventional measuring technology in the case of an ultra-fine process having a critical dimension of no more than about 100 nanometers.
Examples of a fatal process defect due to the reduced critical dimension include a void in an insulation interlayer and a bridge defect in a contact structure for a metal wiring or a stacked capacitance. Typically, an optical instrument or an electron beam has been utilized for measuring the fatal process defects. However, the scaling down of the critical dimension leads to difficulty in measuring the defects.
In general, the fatal process defects are shown in a pattern profile while patterning a layer on a substrate, such that various research has been conducted for analyzing a structure of a vertical profile of the pattern. A vertical scanning electron microscope (V-SEM) and a transmission electron microscope (TEM) have been used for analyzing the vertical profile of the pattern and forming a three-dimensional pattern profile. In the V-SEM, an electron beam is projected to a cross sectional surface of a pattern cut along a vertical line, and thereby detects secondary electrons generated from the cross sectional surface of the pattern. The detected secondary electrons generate an electrical signal, and an image corresponding to the cross sectional surface of the pattern is formed from the electrical signal. In the TEM, an electron beam is also projected to a cross sectional surface of a pattern cut along a vertical line, and tunnel electrons generated from the cross sectional surface of the pattern are detected. An image corresponding to the cross sectional surface of the pattern is formed corresponding to a voltage variance due to the tunnel electrons.
The V-SEM and TEM are advantageous in that they have superior analysis performance with a high degree of precision. However, they also have a disadvantage in that a sample pattern is required for the implementation of these microscopes and thereby requires the sample pattern to be broken down through a destructive analysis. Furthermore, the use of V-SEM and TEM require large expenditures of time to achieve the analysis. That is, the use of V-SEM and the TEM are problematic in that the specimen for the analysis is broken down (e.g., is fractured) and is disposed of after the analysis. Recently, an optical method has been introduced for this type of analysis; however, the method is problematic in that the process and calculation on processing data are very complicated and too cumbersome to apply to a practical analysis on the vertical pattern profile.
Accordingly, there is still need for an improved method of forming a three-dimensional profile of a pattern, or alternatively, a three-dimensional vertical image of a pattern that does not require the fracturing the sample pattern.